The present invention relates to injection cartridges and methods for filling the same with medicament. More specifically, the invention relates to injection cartridges or medicine delivery units for needleless hypodermic (subcutaneous) injectors, i.e., devices for delivering into a body a dose of liquid medicament by way of a fine high pressure liquid stream which penetrates the skin, and methods for filling the cartridges with medicament.
For years, health workers have administered medicine to patients using syringes and needles. (It is to be understood that "medicine" and "medicament" as used herein refers generally to any type of liquid medicament or vaccine.) However, the use of syringes and needles puts health workers and patients at risk of infection through inadvertent needle-sticks or equipment misuse. In addition, syringes and needles are difficult to disinfect or sterilize, and the use of improperly sterilized syringes and needles greatly increases the risk of blood-borne disease transmission among injection recipients. Still further, syringes and needles can cause a high level of anxiety in certain patients, and reuse of dull needles can cause extreme discomfort to the injection recipient.
Disposable syringes and needles have been used to alleviate the risk of disease transmission. However, these disposable units create hazardous waste and waste disposal problems. Inadvertent painful needle sticks and consequent spread of disease and infection may result from the handling of such medical waste. In addition, particularly in some areas of the world where disposable syringes and needles often do not reach the users in adequate quantities, the disposable units may be used more than once, contrary to their intended purpose. A further drawback to disposable needles and syringes is the high costs when the units are provided for widespread use.
Several types of needleless injectors have been developed to avoid some of the drawbacks of syringes and needles. Mass-campaign jet injectors, such as the PEDOJET.TM., have been used to provide fast and efficient needleless injections. However, these units are very difficult to clean or sterilize upon contamination. In addition, the mass-campaign injectors utilize a complex fluid path with dead space therein, such that a substantial amount of residual medicine is retained in the fluid path. When changing from one injectant to another, the residual fluid must be cleared to prevent unacceptable mixing of medicines. This clearing process wastes a relatively large amount of medicine before the injector is ready to inject another patient. Low-workload jet injectors, such as the VITAJET.TM. or the SICIM.TM. HYPODERMIC INJECTOR JET 2000, have also been used to provide needleless injections. These low-workload injectors also utilize a complex fluid path that retains residual medicine. Accordingly, the units are difficult to sterilize, and medicine is wasted through purging when changing between medicines to be administered.
Commonly assigned U.S. patent application Ser. No. 08/483,192, filed Jun. 7, 1995, now U.S. Pat. No. 5,746,714 (hereby incorporated by reference in its entirety), discloses an air-powered needleless hypodermic injector (hereinafter "APNHI") representing a significant improvement over previous designs in several respects. In particular, the injector includes a reusable (primarily stainless steel) medicine delivery unit. The delivery unit mounts in the front end of a main injector housing and is easily removed from the main injector housing for cleaning and/or sterilization, without the need for disassembly of the delivery unit.
A medicine chamber of the APNHI medicine delivery unit receives medicine from a medicine filling mechanism (including a medicine vial) through a unique side-loading fill port. A discharge piston is slidably mounted in the chamber and has a rear rod extension which engages with an air piston driven by a relatively low-pressure air source. During an injection, the air piston drives the discharge piston forward to force medicine in the chamber through an injection nozzle located at the distal end of the chamber, to form a high pressure injection stream. The design provides a simple, removable fluid path with essentially no dead space, and thereby allows medicines to be changed without purging waste. The provision of a side-loading fill port avoids cumbersome arrangements for filling the medicine delivery chamber through the front injection orifice, and the associated increased possibility of surface contamination, as exists in many other devices. In addition, since the side-loading fill port is located very close to the piston head when the piston is in its retracted position, the fill port is closed at the beginning of the piston's discharge stroke. Such positioning of the fill port eliminates the requirement (present in the rear-loading arrangements of other devices) of check-valves to prevent medicine from flowing out of the fill port during the discharge stroke. Such check valves increase costs and are subject to malfunction and leakage due to their repeated exposures to the extremely high injection pressures (e.g., 3000 psi) generated within the chamber.
In certain settings, such as mass immunization campaigns conducted away from health care facilities, it may be inconvenient or impractical to frequently perform cleanings and sterilization of injector components, e.g., the medicine delivery unit of the APNHI. In such settings, it would be highly desirable to be able to employ a low cost disposable medicine delivery unit that would reduce the need for equipment sterilizations.
Copending U.S. application Ser. No. 08/819,563, filed Mar. 14, 1997 (hereby incorporated by reference in its entirety) discloses a single use needleless medicine delivery unit formed of medical grade or commodity polymer. Similar to the medicine delivery unit of U.S. Pat. No. 5,746,714, the delivery unit employs a side-loading fill port for filling the delivery unit at the time of use, through a medicine vial and distributor forming part of the injector. Single use is ensured by the provision of means for positively disabling the medicine delivery unit after a single use, e.g., by retaining the plunger at the end of its injection stroke within a reduced diameter portion of the chamber and/or destroying the injection orifice with a protrusion at the distal end of the slidable piston seal.
The side-load port arrangements described in the '714 patent and application Ser. No. 08/819,563 have substantial advantages over previous known arrangements. However, like known rear-fill methods/arrangements, in order to completely fill the chamber of the delivery unit (leaving no air space) it is necessary to purge air from the chamber. This is typically done by forcing medicament into the chamber under pressure to the point where leakage (dribbling) from the unobstructed discharge outlet (nozzle orifice) occurs.
For certain applications, rather than filling the medicine deliver unit (injection cartridge) at or just prior to the time of injection, it is preferable to utilize pre-filled injection cartridges. This permits simplification of the injection apparatus and procedure, because the means and steps for delivery of medicine to the cartridge can be dispensed with. While transferring liquids into vials is a standard packaging practice of pharmaceutical companies, the pre-filling of unit dose injection cartridges has proven problematic. It is relatively easy to fill a cartridge if the cartridge is sealed at its distal end (e.g., nozzle face), inverted and left open at its proximal end. However, in order to seal the fluid chamber, a plug, cap or piston seal must then be forced into place, at the proximal end, against the sealed fluid. This can result in fluid spills and can slow a packaging line. Ideally, a unit dose injection cartridge would allow fluid medicament to be metered easily into the chamber, and then the chamber to be sealed, without requiring additional cumbersome steps for proper placement of the piston seal after filling of the chamber.